The present invention relates to a flocculant for separating and flocculating oil and water. More particularly, the present invention relates to a flocculant for separating and flocculating oily components and water components contained in oil-in-water type or water-in-oil type emulsion, and a method for separating and flocculating oil and water.
Water lubricants are widely utilized in the iron and steel manufacturing and machining art. The water lubricants are advantageous in that they are incombustible, inexpensive, nontoxic, and safety, and have excellent cooling, viscosity changing, and compression properties as compared with petroleum lubricants. Accordingly, the water lubricants are widely used as oil-in-water type or water-in-oil type emulsion in cutting oil and grinding fluid. With an increase in the use of the water lubricants, it becomes a problem how to treat a waste water lubricant or waste liquid containing such water lubricants.
Conventionally, the waste water lubricant or the waste liquid is separated and flocculated with a flocculant as a primary treatment. For example, there is an inorganic flocculant such as aluminum sulfate referred to as “sulfate band”, and poly(aluminum chloride) referred to as “pack”, and an organic flocculant such as polyacrylic amide based polymer. These flocculants are added to the waste water lubricant or the waste liquid to break the emulsion, whereby the oily components and the water components are separated.
The separated water components are secondary treated, for example, by an active sludge treatment.
Japanese Patent Laid-Open Application No. 11-33309 describes an organic flocculant terminated at their molecular ends with —OSO3M groups that do not reduce throughput of the active sludge.
When the inorganic flocculant is used in the primary treatment, the pH of the water lubricant is often decreased. It requires to neutralize it with alkali such as caustic soda. This may undesirably result in complex processes, and increased costs.
In addition, the inorganic flocculant absorbs and precipitates the waste while producing a large amount of colloidal particles. Therefore, a large amount of the inorganic flocculant is required. As a result, a large amount of sludge is produced, whereby the disposal costs for the sludge are undesirably increased.
Furthermore, the inorganic flocculant may adversely affect the secondary treatment of the active sludge. For example, when the remaining inorganic flocculant is deposited on the active sludge, an oxygen consumption rate of the active sludge is reduced, or the sludge is partially decomposed, whereby the throughput of the active sludge is reduced.
On the other hand, an amount of the organic flocculant such as polyacrylic amide based polymer is as low as ½ to 1/200 of that of the inorganic flocculant used in the active sludge treatment. However, the organic flocculant less removes the oily components and a surfactant, and therefore undesirably decreases the throughput of the active sludge.
Even if the organic flocculant is terminated at their molecular ends with —OSO3M groups, a chemical oxygen demand (COD) of the waste water is less decreased, when the waste water has a high COD value.
When oil and water is separated in the oil and water separating step, mayonnaise-like sludge is produced at an interface of the oil and the water. The mayonnaise-like sludge may sometimes be separated in several hours. Typically, the separation of the oil and the water takes a longer time. A water content in an oily layer unfavorably increases.